Projection TV with improved micromirror array

ABSTRACT

In order to minimize light diffraction along the direction of switching and more particularly light diffraction into the acceptance cone of the collection optics, in the present invention, micromirrors are provided which are not rectangular. Also, in order to minimize the cost of the illumination optics and the size of the display unit of the present invention, the light source is placed orthogonal to the rows (or columns) of the array, and/or the light source is placed orthogonal to a side of the frame defining the active area of the array. The incident light beam, though orthogonal to the sides of the active area, is not however, orthogonal to any substantial portion of sides of the individual micromirrors in the array. Orthogonal sides cause incident light to diffract along the direction of micromirror switching, and result in light ‘leakage’ into the ‘on’ state even if the micromirror is in the ‘off’ state. This light diffraction decreases the contrast ratio of the micromirror. The micromirrors of the present invention result in an improved contrast ratio, and the arrangement of the light source to micromirror array in the present invention results in a more compact system. Another feature of the invention is the ability of the micromirrors to pivot in opposite direction to on and off positions (the on position directing light to collection optics)-, where the movement to the on position is greater than movement to the off position. A further feature of the invention is a package for the micromirror array, the package having a window that is not parallel to the substrate upon which the micromirrors are formed. One example of the invention includes all the above features.

This is a continuation of Ser. No. 10/343,307 filed Jan. 29, 2003 nowU.S. Pat. No. 6,962,419 which is U.S. National Phase of PCT/US01/24332filed Aug. 3, 2001, which claims priority from Ser. No. 09/631,536 filedAug. 3, 2000 (now U.S. Pat. No. 6,529,310) and 60/229,246 filed Aug. 30,2000, and Ser. No. 09/732,445 filed Dec. 7, 2000 (now U.S. Pat. No.6,523,961), each of the above applications being incorporated herein byreference.

BACKGROUND Summary of the Invention

In order to minimize light diffraction along the direction of switchingand in particular light diffraction into the acceptance cone of thecollection optics, in the present invention, micromirrors are providedwhich are not rectangular (“rectangular” as used herein including squaremicromirrors). Diffraction as referred to herein, denotes the scatteringof light off of a periodic structure, where the light is not necessarilymonochromatic or phase coherent. Also, in order to minimize the cost ofthe illumination optics and the size of the display unit of the presentinvention, the light source is placed orthogonal to the rows (orcolumns) of the array, and/or the light source is placed orthogonal to aside of the frame defining the active area of the array. The incidentlight beam, though orthogonal to the rows (or columns) and/or side ofthe active area, should not, however, be orthogonal to sides of theindividual micromirrors in the array. Orthogonal sides cause incidentlight to diffract along the direction of micromirror switching, andresult in light ‘leakage’ into the ‘on’ state even if the micromirror isin the ‘off’ state. This light diffraction decreases the contrast ratioof the micromirror.

The present invention optimizes the contrast ratio of the micromirrorarray so that when micromirrors are in their ‘off’ state they sendminimal light to the spatial region where light is directed whenmicromirrors are in their ‘on’ state. More specifically, the presentinvention comprises a particularly located light source and incidentlight beam and particularly designed micromirrors in the array, whichminimize light diffracted into the acceptance cone of the projection (orviewing) optics, so as to provide an improved contrast ratio. Thearrangement and design of the present invention also minimizesnon-reflective areas in the array, by allowing for a tight fit ofmicromirrors and a large fill factor with low diffraction from the ‘off’to the ‘on’ state, even when the array is illuminated along the axes ofmicromirror periodicity. Namely, the design optimizes contrast ratiothrough angular sides non-parallel to the micromirror's axis of rotationand optimizes fill factor through hinges that require a relatively smallamount of area and allow neighboring micromirrors to tile together withlittle wasted non-reflective area. The micromirror structures and shapesof various examples of the invention also decrease cross talk betweenadjacent micromirrors when the micromirrors are deflectedelectrostatically.

Another aspect of the invention is a micromirror array where theindividual micromirrors tilt asymmetrically around a flat ornon-deflected state. By making the ‘off’ state of the micromirrors at anangle less than the opposite angle of the micromirrors in the ‘on’state, a) diffracted light from the edges of the micromirrors thatenters the collection optics is minimized, b) and light that isscattered from beneath the micromirrors that enters the collectionoptics is also minimized, c) travel of the micromirrors is decreasedthus minimizing the possibility of adjacent micromirrors hitting eachother, which in turn allows for reducing the gap between micromirrorsand increasing fill factor of the micromirror array, and d) the angle ofdeflection of the micromirrors can be increased to a greater extent thanmicromirror array arrangements with the same angle of deflection for theon and off states.

Another aspect of the invention is a package for the micromirror arraythat has a light transmissive portion of the package that is notparallel with the substrate upon which the micromirrors are formed. Thelight transmissive portion can be any suitable material such as a plateof glass, quartz or polymer, and allows for directing specularreflection from the light transmissive substrate in directions otherthan those that result from a parallel light transmissive plate in thepackaging. Preferably the specular reflection is directed sufficientlyfar from the collection optics so that an increase in the size of theillumination cone will keep the specular reflection from entering thecollection optics.

A further aspect of the invention is a projection system, comprising anarray of active micromirrors disposed in a rectangular shape, themicromirrors capable of rotation around a switching axis between anoff-state and an on-state, the micromirrors corresponding to pixels in aviewed image; a light source for directing light to the array ofmicromirrors, the light source disposed so as to direct lightnon-perpendicular to at least two sides of each micromirror, andparallel, when viewed as a top view of each micromirror, to at least twoother sides of each micromirror; and collection optics disposed toreceive light from micromirrors in an on-state.

Another aspect of the invention is a projection system, comprising anarray of micromirrors, each micromirror corresponding to a pixel in aviewed image and having a shape of a concave polygon or one or morenon-rectangular parallelograms; a light source for directing light tothe array of micromirrors collection optics disposed to receive lightreflected from the micromirrors.

Yet another aspect of the invention is a projection system comprising alight source for providing an incident light beam, an array of movablereflective elements, and collection optics for projecting light from thearray, wherein an image projected from the projection system will appearon a target as a rectangular image, with the image being formed of fromthousands to millions of pixels, each pixel being in the shape of aconcave polygon, a single non-rectangular parallelogram, or an assemblyof non-rectangular parallelograms.

Still another aspect of the invention is a projection system comprisinga light source, an array of movable micromirror elements, and collectionoptics, wherein each micromirror element in the array has a switchingaxis substantially parallel to at least one side of the active area ofthe array, and at an angle of from 35 to 60 degrees to one or more sidesof the micromirror element.

Another aspect of the invention is a projection system comprising alight source and an array of movable micromirror elements, eachmicromirror element having a leading side that is non-perpendicular tothe incident light beam, and non-perpendicular to any side of the activearea, so as to achieve an increase of 2 to 10 times the contrast ratiocompared to micromirror elements having perpendicular sides to theincident light beam.

Another aspect of the invention is a projection system comprising alight source, collection optics, and an array of movable micromirrorelements, the projection system having a diffraction patternsubstantially the same as that illustrated in FIG. 21C.

Yet another aspect of the invention is a projection system comprising alight source and a rectangular array of movable micromirrors, themicromirrors capable of moving between an on-state and an off-state andcapable of reflecting light in the on-state to a predetermined spatialarea, wherein the light source is disposed to direct light at asubstantially 90 degree angle to at least one side of the rectangledefined by the array, and wherein substantially no diffracted lightenters the predetermined spatial area when the micromirrors are in theoff-state.

Another aspect of the invention is a method for projecting an image on atarget comprising: directing a light beam onto a rectangular array ofmicromirrors, the light beam directed to the leading side of therectangular array at an angle within a range of 90 degrees plus or minus40 degrees, and wherein the micromirrors in the array are shaped aspolygons and positioned such that the light beam is incident on all ofthe polygonal sides at angles other than 90 degrees; and projecting thelight from the micromirrors onto a target so as to form an imagethereon.

Another part of the invention is a projection system comprising a lightsource, light collection optics and an array of micromirrors disposed tospatially modulate a light beam from the light source, the array formedon a substrate and constructed so that each micromirror is capable ofbeing in a first position when not actuated, each micromirror beingcapable of movement to an on position that directs light to lightcollection optics for the array, and capable of movement in an oppositedirection to an off position for directing light away from the lightcollection optics, both said on and off positions being different fromsaid first position, and wherein the on position is at an angle relativeto the first position different from the off position.

Still another aspect of the invention is a method for spatiallymodulating a light beam, comprising directing a light beam from a lightsource to light collection optics via an array of micromirrors disposedto spatially modulate the light beam from the light source, the arrayformed on a substrate and each micromirror being in a first positionwhen not modulated, modulating micromirrors in the array so that eachmicromirror moves to an on position that directs light to the lightcollection optics for the array, and moves to an off position fordirecting light away from the light collection optics, both said on andoff positions being different from said first position, and wherein theon position is at a magnitude of an angle relative to the first positiondifferent from the magnitude of an angle when in the off position.

Still another aspect of the invention is an optical micromechanicalelement formed on a substrate having an on position at a first magnitudeof an angle relative to the substrate, having an off position at asecond magnitude of an angle to the substrate, the first and secondmagnitudes being different, and having a third position substantiallyparallel to the substrate, both the on and off positions being definedby abutment of the optical micromechanical element against the substrateor against structure formed on said substrate.

Yet another aspect of the invention is a method for modulating light,comprising reflecting light from an array of deflectable micromirrorsdisposed on a planar substrate; said micromirrors tilted to either afirst position or to a second position; wherein the angle formed betweensaid first position and the substrate, and the angle formed between saidsecond position and the substrate, are substantially different.

Another part of the invention is a method for modulating light,comprising a light source, a planar light modulator array comprising adeflectable elements and collection optics, wherein the elements in thearray are selectively configured in at least two states, wherein thefirst state elements direct the light from the light source through afirst angle into the collection optics, and in the second state elementsdirect the light from the light source through a second angle into thecollection optics, a third angle representing light that is reflectedfrom the array as if it were a micromirrored surface, wherein thedifference between the first and third and second and third angles aresubstantially different.

Another aspect of the invention is a projection system, comprising alight source for providing a light beam; a micromirror array comprisinga plurality of micromirrors provided in a path of the light beam; andcollection optics disposed in a path of the light beam after the lightbeam is incident on the micromirror array and reflects off of theplurality of micromirrors as a pattern of on and off micromirrors in thearray; wherein the micromirror array comprises a substrate, the array ofmicromirrors being held on the substrate where each micromirror iscapable of moving to an on position and an off position from anon-deflected position, wherein the on position is at a different anglethan the off position relative to the non-deflected position.

Still another part of the invention is a method for projecting an imageonto a target, comprising directing a light beam from a light sourceonto a micromirror array; modulating the micromirrors each to an on oroff position, wherein in the on position, micromirrors direct light tocollection optics disposed for receiving light from micromirrors intheir on position, wherein the pattern of on and off micromirrors formsan image; and wherein the position of the micromirrors in their onposition is at a different magnitude of an angle compared to themagnitude of the angle of the micromirrors in their off position.

Yet another part of the invention is a method for spatially modulating alight beam, comprising directing a beam of light onto an array ofmicromirrors, the micromirrors capable of movement to a first or secondposition, wherein in the first position the micromirrors direct aportion of the beam of light incident thereon into a collection optic,and wherein the minimum distance between adjacent micromirrors when eachin the second position is less than the minimum distance between theadjacent micromirrors when each is in the first position.

Another aspect of the invention is a device comprising a substrate onwhich is formed a movable reflective or diffractive micromechanicaldevice; a package for holding the substrate with the movablemicromechanical device; wherein the package comprises an opticallytransmissive window that is non-parallel to the substrate.

A further part of the invention is a projection system, comprising alight source; light collection optics; a substrate on which is formed amovable reflective or diffractive micromechanical device; a package forholding the substrate with the movable micromechanical device; whereinthe package comprises an optically transmissive window that isnon-parallel to the substrate; the packaged micromechanical devicedisposed in a path of a light beam from the light source for modulatinglight from the light beam, and the collection optics collecting themodulated light.

A still further part of the invention is a projector comprising a lightsource, a packaged MEMS device having a substrate with a micromechanicaldevice thereon and a window in the package disposed at an angle to thesubstrate, and collection optics disposed to receive light from thelight source after modulation by the packaged MEMS device.

Another aspect of the invention is a method for making a micromirror,comprising providing a substrate; depositing and patterning a firstsacrificial layer on the substrate; depositing at least one hinge layeron the sacrificial layer and patterning the at least one hinge layer todefine at least one flexure hinge; depositing and patterning a secondsacrificial layer; depositing at least one mirror layer on the secondsacrificial layer and patterning the at least one mirror layer to form amirror element; and removing the first and second sacrificial layers soas to release the micromirror.

And still yet another aspect of the invention is an opticalmicromechanical device, comprising a substrate; a first post on thesubstrate; a flexure hinge where a proximal end of flexure hinge is onthe post; a second post attached to a distal end of the flexure hinge;and a plate attached to the second post.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of one embodiment of the micromirrors of thepresent invention;

FIGS. 2A to 2E are cross sectional views of one method for making themicromirrors of the present invention, taken along line 2—2 of FIG. 1;

FIGS. 3A to 3D are cross sectional views of the same method shown inFIGS. 2A to 2E, but taken along line 3—3 of FIG. 1;

FIGS. 4A to 4J are cross sectional views illustrating a further methodfor making micromirrors for the present invention;

FIGS. 5A to 5G are cross sectional views illustrating yet a furthermethod for making micromirrors in accordance with the present invention;

FIGS. 6A to 6C are plan views of different micromirror shape and hingecombinations;

FIG. 7 is a plan view of a portion of a micromirror array with multiplemicromirrors the same as in FIG. 6A;

FIG. 8 is a partially exploded isometric view of a micromirror of oneembodiment of the invention;

FIGS. 9A to 9C are cross sectional views showing actuation of amicromirror of the embodiment of FIG. 8;

FIGS. 10A to 10D are cross sectional views of a process in accordancewith yet another embodiment of the invention;

FIGS. 11A to 11C are cross sectional views showing actuation of amicromirror made in accordance with the method illustrated in FIGS. 10Ato 10D;

FIG. 12 is a plan view of multiple micromirrors in a micromirror arrayformed in accordance with the method of FIGS. 11A to 11C;

FIG. 13 is a partially exploded isometric view of the micromirror ofFIG. 12;

FIGS. 14A to 14C illustrate micromirrors having a flat non-deflected‘off’ state;

FIGS. 15A to 15C illustrate micromirrors having deflected ‘on’ and ‘off’states of equal angles;

FIGS. 16A to 16C illustrated micromirrors having a greater angle for the‘on’ state than the ‘off’ state;

FIGS. 17A to 17E illustrate a package arrangement for micromirrorshaving an angled window;

FIG. 18 is an illustration of the illumination system for themicromirror array of the present invention;

FIGS. 19A to 19E illustrate the relationship between angle of incidentlight, micromirror sides, and active area sides;

FIG. 20 is an illustration of a prior art micromirror array;

FIGS. 21 and 22 are illustrations of an embodiment of the inventionwhere square micromirrors are at an angle to the active area sides;

FIGS. 23 to 25 illustrate micromirrors where “leading” and “trailing”edges of the micromirrors are not perpendicular to the incident lightbeam;

FIGS. 26A to 26F and 27A to 27F are illustrations of micromirrors havingthe shapes of one or more parallelograms;

FIG. 28 is an illustration of a single micromirror;

FIG. 29 is an illustration of a micromirror array having part of theleading and trailing sides perpendicular to the incident light beam, andanother part at a 45 degree angle to the incident light beam;

FIGS. 30 and 31 are illustrations of micromirror arrays where themicromirrors have no sides parallel or perpendicular to the incidentlight beam or the sides of the active area of the array;

FIGS. 32A to 32J are illustrations of micromirrors with correspondinghinge structures; and

FIGS. 33A to 33C are illustrations of diffraction patterns having adiffraction line passing through the acceptance cone of the collectionoptics (33A) and avoiding the acceptance cone (33B and 33C).

DETAILED DESCRIPTION

Processes for microfabricating a movable micromirror or micromirrorarray are disclosed in U.S. Pat. Nos. 5,835,256 and 6,046,840 both toHuibers, the subject matter of each being incorporated herein byreference. A similar process for forming the micromirrors of the presentinvention is illustrated in FIGS. 1 to 3. FIG. 1 is a top view of oneembodiment of the micromirrors of the present invention. As can be seenin FIG. 1, posts 21 a and 21 b hold micromirror plate 24 via hinges 120a and 120 b above a lower substrate having electrodes thereon (notshown) for causing deflection of micromirror plate 24. Though not shownin FIG. 1, and as will be discussed further herein, thousands or evenmillions of micromirrors 24 can be provided in an array for reflectinglight incident thereon and projecting an image to a viewer ortarget/screen.

Micromirror 24, and the other micromirrors in the array, can befabricated by many different methods. One method is illustrated in FIGS.2A to 2E (taken along cross section 2—2 from FIG. 1) where themicromirrors are fabricated on preferably a light transmissive substratewhich is then bonded to a circuit substrate. This method is disclosedfurther in U.S. Provisional Patent Application 60/229,246, to Ilkov etal., filed Aug. 30, 2000, and U.S. patent application Ser. No.09/732,445 to Ilkov et al., filed Dec. 7, 2000. Though the method willbe describe in connection with a light transmissive substrate, any othersuitable substrate could be used, such as a semiconductor substrate withcircuitry. If a semiconductor substrate such as single crystal siliconis used, it may be preferred to electrically connect the micromirrorposts to the metal 3 layer in the IC process and utilize conductivematerials for at least a part of the micromirrors. Methods of formingmicromirrors directly on a circuit substrate (instead of on a separatelight transmissive substrate) will be discussed in more detail furtherherein.

As can be seen in FIG. 2A, a light transmissive substrate 13 (at leastprior to adding further layers thereon) such as glass (e.g., Corning1737F or Eagle2000), quartz, Pyrex™, sapphire, etc. is provided. Thelight transmissive substrate can have an optional light blocking layeradded on its lower side to help in handling the substrate duringprocessing. Such a light blocking layer could be a TiN layer depositedby reactive sputtering to a depth of 2000 angstroms on the back side ofthe light transmissive substrate, which would later be removed onceprocessing is complete. The substrate can be any shape or size, thoughone that is the shape of a standard wafer used in an integrated circuitfabrication facility is preferred.

As can also be seen in FIG. 2A, a sacrificial layer 14, such asamorphous silicon, is deposited. The sacrificial layer can be anothersuitable material that can later be removed from under themicromechanical structural materials (e.g., SiO2, polysilicon,polyimide, novolac, etc.). The thickness of the sacrificial layer can bewide ranging depending upon the movable element/micromirror size anddesired tilt angle, though a thickness of from 500 Å to 50,000 Å,preferably around 5000 Å is preferred. Alternative to the amorphoussilicon, the sacrificial layer could be any of a number of polymers,photoresist or other organic material (or even polysilicon, siliconnitride, silicon dioxide, etc. depending upon the materials selected tobe resistant to the etchant, and the etchant selected). An optionaladhesion promoter (e.g., SiO2 or SiN) can be provided prior todepositing the sacrificial material.

Hole 6 having width “d” is formed in the sacrificial layer in order toprovide a contact area between the substrate 13 and later depositedmicromechanical structural layers. The holes are formed by spinning on aphotoresist and directing light through a mask to increase or decreasesolubility of the resist (depending upon whether the resist is apositive or negative resist). Dimension “d” can be from 0.2 to 2micrometers (preferably around 0.7 um), depending upon the ultimate sizeof the micromirror and the micromirror array. After developing theresist to remove the resist in the area of the holes, the holes areetched in the sacrificial amorphous silicon with a chlorine or othersuitable etchant (depending upon the sacrificial material). Theremaining photoresist is then removed, such as with an oxygen plasma.The hole in the sacrificial layer can be any suitable size, thoughpreferably having a diameter of from 0.1 to 1.5 um, more preferablyaround 0.7+/−0.25 um. The etching is performed down to the glass/quartzsubstrate or down to any intermediate layers such as adhesion promotinglayers. If the light transmissive substrate is etched at all, it ispreferably in an amount less than 2000 Å. If the sacrificial layer 14 isa directly patternable material (e.g., a novolac or other photosensitivephotoresist) then an additional layer of photoresist deposited anddeveloped on top of the sacrificial layer 14 is not needed. In such acase, the photoresist sacrificial layer is patterned to remove materialin the area of hole(s) 6 and then optionally hardened before depositingadditional layers.

At this point, as can be seen in FIG. 2B, a first structural layer 7 isdeposited by, e.g., chemical vapor deposition. Preferably the materialis silicon nitride or silicon oxide deposited by LPCVD (low pressurechemical vapor deposition) or PECVD (plasma enhanced chemical vapordeposition), however any suitable thin film material such aspolysilicon, a metal or metal alloy, silicon carbide or an organiccompound could be deposited at this point (of course the sacrificiallayer and etchant should be adapted to the structural material(s) used).The thickness of this first layer can vary depending upon the movableelement size and desired amount of stiffness of the element, however inone embodiment the layer has a thickness of from 100 to 3200 Å, morepreferably between 900 and 1100 Å. As can be seen in FIG. 2B, layer 7extends into the holes etched in the sacrificial layer.

A second layer 8 is deposited as can be seen in FIG. 2C. The materialcan be the same (e.g., silicon nitride) as the first layer or different(silicon oxide, silicon carbide, polysilicon, etc.) and can be depositedby chemical vapor deposition as for the first layer. The thickness ofthe second layer can be greater or less than the first, depending uponthe desired stiffness for the movable element, the desired flexibilityof the hinge, the material used, etc. In one embodiment the second layerhas a thickness of from 50 Å to 2100 Å, and preferably around 900 Å. Inanother embodiment, the first layer is deposited by PECVD and the secondlayer by LPCVD.

In the embodiment illustrated in FIGS. 2A to 2E, both the first andsecond layers are deposited in the areas defining the movable(micromirror) element and the posts. Depending upon the desiredstiffness for the micromirror element, it is also possible to depositonly one of the first or second layers in the area of the micromirrorelement. Also, a single layer could be provided in place of the twolayers 7, 8 for all areas of the microstructure, though this couldinvolve a tradeoff in plate stiffness and hinge flexibility. Also, if asingle layer is used, the area forming the hinge could be partiallyetched to lower the thickness in this area and increase the flexibilityof the resulting hinge. It is also possible to use more than two layersto produce a laminate movable element, which can be desirableparticularly when the size of the movable element is increased such asfor switching light beams in an optical switch. The materials for suchlayer or layers could also comprise alloys of metals and dielectrics orcompounds of metals and nitrogen, oxygen or carbon (particularly thetransition metals). Some of these alternative materials are disclosed inU.S. Provisional Patent Application No. 60/228,007, the subject matterof which is incorporated herein by reference.

As can be seen in FIG. 2D, a reflective layer 9 is deposited. Thereflective material can be gold, silver, titanium, aluminum or othermetal, or an alloy of more than one metal, though it is preferablyaluminum deposited by PVD. The thickness of the metal layer can be from50 to 2000 Å, preferably around 500 Å. An optional metal passivationlayer (not shown) can be added, e.g., a 10 to 1100 Å silicon oxide layerdeposited by PECVD on top of layer 9. Other metal deposition techniquescan be used for depositing metal layer 9, such as chemical fluiddeposition and electroplating. After depositing layer 9, photoresist isspun on and patterned, followed by etching of the metal layer with asuitable metal etchant. In the case of an aluminum layer, a chlorine (orbromine) chemistry can be used (e.g., a plasma/RIE etch with Cl₂ and/orBCl₃ (or Cl2, CCl4, Br2, CBr₄, etc.) with an optional preferably inertdiluent such as Ar and/or He). It should be noted that the reflectivelayer need not be deposited last, but rather could be deposited directlyupon the sacrificial layer 14, between other layers defining themicromirror element, or as the only layer defining the micromirrorelement. However, in some processes it may be desirable to deposit ametal layer after a dielectric layer due to the higher temperature atwhich many dielectrics are deposited.

Relating to FIG. 2E, the first and second layers 7, 8 can be etchedsubsequent to the reflective layer with known etchants or combinationsof etchants (depending upon the material used and level of isotropydesired). For example, the first and second layers can be etched with achlorine chemistry or a fluorine (or other halide) chemistry (e.g., aplasma/RIE etch with F₂, CF₄, CHF₃, C₃F₈, CH₂F₂, C₂F₆, SF₆, etc. or morelikely combinations of the above or with additional gases, such asCF₄/H₂, SF₆/Cl₂, or gases using more than one etching species such asCF₂Cl₂, all possibly with one or more optional inert diluents). Ofcourse, if different materials are used for the first layer and thesecond layer, then a different etchant can be employed for etching eachlayer (plasma etching chemistry known in the art depending upon thematerials used). If the reflective layer is deposited before the firstand second layers, the etching chemistries used would be reversed. Or,depending upon the materials used, all layers could be etched together.Gaps 20 a and 20 b having a width “e” shown in FIG. 2E are forseparating the post 21 from the micromirror body 22.

FIGS. 3A to 3D illustrate the same process taken along a different crosssection (cross section 3—3 in FIG. 1) and show the light transmissivesubstrate 13, on which is deposited a sacrificial layer 14. Onsacrificial layer 14 is deposited structural layer 7. As can be seen inFIGS. 3B and 3C, a part of layer 7 is removed prior to adding layers 8and 9. This portion removed is in the area where the hinge is to beformed, and allows for increased flexibility in the hinge area. This“thinning” of the hinge area in this way, is set forth in U.S.Provisional Patent Application No. 60/178,902 to True et al., filed Jan.28, 2000, and in U.S. patent application Ser. No. 09/767,632 to True etal., filed Jan. 22, 2001, the subject matter of each incorporated hereinby reference. After removing portions of layer 7, layers 8 and 9 areadded, followed by patterning of layers 7, 8 and 9 as set forth above.As can be seen in FIG. 3D, hinges 23 have width “a” that can be from 0.1to 10 um, preferably around 0.7 um. The hinges 23 are separated fromeach other by a gap “b” and from adjacent micromirror plates by gaps “c”that also can be from 0.1 to 10 um, preferably around 0.7 um.

The process steps mentioned generally above, can be implemented in anumber of ways. For example, a glass wafer (such as a Corning 1737F,Eagle 2000, quartz or sapphire wafer) can be provided and coated with anopaque coating, such as a Cr, Ti, Al, TaN, polysilicon or TiN or otheropaque coating at a thickness of 2000 angstroms (or more depending uponthe material) on the backside of the wafer, in order to make thetransparent substrate temporarily opaque for handling. Then, inaccordance with FIGS. 1–4, after an optional adhesion layer is deposited(e.g., a material with dangling silicon bond such as SiNx—or SiOx, or aconductive material such as vitreous carbon or indium tin oxide) then asacrificial material of hydrogenated amorphous silicon is deposited(gas=SiH4 (200 sccm), 1500 sccm of Ar, power=100 W, pressure=3.5 T,temp=380 C, electrode spacing=350 mil; or gas=150 sccm of SiHy, 100 sccmof Ar, power=55 W, pressure=3 Torr, temp=380 C, electrode spacing=350mil; or gas=200 sccm SiH4, 1500 sccm Ar, power=100 W, temp=300 C,pressure=3.5 T; or other process points in between these settings) onthe transparent wafer at a thickness of 5000 Angstroms in a plasmaenhanced chemical vapor deposition system such as an Applied MaterialsP5000. Or, the sacrificial material could be deposited by LPCVD at 560C, along the lines set forth in U.S. Pat. No. 5,835,256 to Huibers etal., incorporated herein by reference. Or, the sacrificial materialcould be deposited by sputtering, or could be a non-silicon containingmaterial such as an organic material (to be later removed by, e.g.,plasma oxygen ash). The a-Si is patterned (photoresist and etched by achlorine chemistry, e.g., Cl2, BCl3 and N2), so as to form holes forattachment of the micromirror to the glass substrate. A first layer ofsilicon nitride, for creating stiffness in the micromirror and forconnecting the micromirror to the glass, is deposited by PECVD (RFpower=150 W, pressure=3 Torr, temp=360 C, electrode spacing=570 mils,gas =N2/SiH4/NH3 (1500/25/10); or RF power=127 W, pressure=2.5 T,temp=380 C, gas =N2SiH4/NH3 (1500/25/10 sccm), electrode spacing=550mil, or other process parameters could be used, such as power at 175 Wand pressure at 3.5 Torr) at a thickness of 900 Angstroms and ispatterned (pressure=800 mT, RF power=100 to 200 W, electrode spacing=0.8to 1.1 mm, gas =CF4/CHF3/Ar (60 or 70/40 to 70/600 to 800 sccm, He=0 to200 sccm), so as to remove the silicon nitride in areas in which themicromirror hinges will be formed. Next, a second layer of siliconnitride is deposited by PECVD (RF power=127 W, pressure=2.5 T, temp=380C, gas =N2/SiH4/NH3 (1500/25/10 sccm), electrode spacing=550 mil) at athickness of 900 Angstroms. Then, Al is sputtered onto the secondsilicon nitride layer at a thickness of 500 Angstroms at a temp of from140 to 180 C, power=2000 W, Ar=135 sccm. Or, instead of Al, the materialcould be an aluminum alloy (Al—Si (1%), Al—Cu (0.5%) or AlSiCu or AlTi),as well as an implanted or target doped aluminum. The aluminum ispatterned in the P5000 with a chlorine chemistry (pressure=40 mT,power=550 W, gas=BCl3/Cl2/N2=50/15/30 sccm). Then, the SiN layers areetched (pressure=100 mT, power=460 W, gas =CF4/N2 (9/20 sccm)), followedby ashing in a H2O+O2+N2 chemistry in plasma. Next, the remainingstructures are ACT cleaned (acetone+DI wafer solution) and spun dry.(This clean can also be done with EKC Technology's EKS265 photoresistresidue remover or other solvent based cleaner). After resist coatingthe frontside of the wafer having the microstructures thereon, thebackside TiN is etched in a BCl3/Cl2/CF4 chemistry in plasma (or othermetal etchant from CRC Handbook of Metal Etchants)—or polished or groundoff using CMP, or removed with acid vapor such as HF—followed by asecond ACT clean (acetone+DI wafer solution) and a second spin dry. Thewafer is singulated into individual die and each die is exposed to 300 WCF4 plasma (pressure=150 Torr, 85 sccm for 60 seconds, followed by 300sec etch in a mixture of He, XeF2 and N2 (etch pressure 158 Torr). Theetch is performed by providing the die in a chamber of N2 at around 400Torr. A second area/chamber has therein 3.5 Torr XeF2 and 38.5 Torr He.A barrier between the two areas/chambers is removed, resulting in thecombined XeF2, He and N2 etching mixture.

Or, the transparent wafer (e.g., Corning 1737F) is coated with TiN at athickness of 2000 angstroms on the backside of the glass wafer. Then, inaccordance with FIGS. 1–4, without an adhesion layer, a sacrificialmaterial of hydrogenated amorphous silicon is deposited (power=100 W,pressure=3.5 T, temp=300 C, SiH4=200 sccm, Ar=1500 sccm, or pressure=2.5Torr, power=50 W, temp=360 C, electrode spacing=350 mils, SiH4 flow =200sccm, Ar flow=2000 sccm) on a glass wafer at a thickness of 5300Angstroms in an Applied Materials P5000. The a-Si is patterned(photoresist and etched by a chlorine chemistry, e.g., Cl2, BCl3 andN2–50 W), so as to form holes for attachment of the micromirror to theglass substrate. A first layer of silicon nitride, for creatingstiffness in the micromirror and for connecting the micromirror to theglass, is deposited by PECVD (pressure=3 Torr, 125 W, 360 C, gap=570,SiH4=25 sccm, NH3=10 sccm, N2=1500 sccm)) at a thickness of 900Angstroms and is patterned (CF4/CHF3), so as to remove the siliconnitride in areas in which the micromirror hinges will be formed. Next, asecond layer of silicon nitride is deposited by PECVD (same conditionsas first layer) at a thickness of 900 Angstroms. Then, Al is sputtered(150 C) onto the second silicon nitride layer at a thickness of 500Angstroms. The aluminum is patterned in the P5000 with a chlorinechemistry (BCl3, Cl2, Ar). Then, the SiN layers are etched (CHF3, CF4),followed by ashing in a barrel asher (O2, CH3OH at 250 C). Next, theremaining structures are cleaned with EKC Technology's EKS265photoresist residue remover. After resist coating the frontside of thewafer having the microstructures thereon, the backside TiN is etched ina SF6/Ar plasma, followed by a second clean and a second spin dry.

After depositing the sacrificial and structural layers on a wafersubstrate, the wafer is singulated and each die then is placed in aDrytek parallel plate RF plasma reactor. 100 sccm of CF4 and 30 sccm ofO2 flow to the plasma chamber, which is operated at about 200 mtorr for80 seconds. Then, the die is etched for 300 seconds at 143 Torr etchpressure (combined XeF2, He and N2). The etch is performed by providingthe die in a chamber of N2 at around 400 Torr. A second area/chamber hastherein 5.5 Torr XeF2 and 20 Torr He. A barrier between the twoareas/chambers is removed, resulting in the combined XeF2, He and N2etching mixture. The above could also be accomplished in a parallelplate plasma etcher with power at 300 W CF4 (150 Torr, 85 sccm) for 120seconds. Additional features of the second (chemical, non-plasma) etchare disclosed in U.S. patent application Ser. No. 09/427,841 to Patel etal., filed Oct. 26, 1999, and U.S. patent application Ser. No.09/649,569 to Patel et al. filed Aug. 28, 2000, the subject matter ofeach being incorporated herein by reference.

Though the hinge of each micromirror can be formed essentially in thesame plane as the micromirror element (layers 7, 8 and 9 for themicromirror body vs. layers 8 and 9 for the micromirror hinge in FIG.3D) as set forth above, they can also be formed separated from andparallel to the micromirror element in a different plane and as part ofa separate processing step (after deposition of a second sacrificialmaterial). This superimposed type of hinge is disclosed in FIGS. 8 and 9of the previously-mentioned U.S. Pat. No. 6,046,840, and in more detailin U.S. patent application Ser. No. 09/631,536 to Huibers et al., filedAug. 3, 2000, the subject matter of which being incorporated herein byreference. Whether formed with one sacrificial layer as in the Figures,or two (or more) sacrificial layers as for the superimposed hinge, suchsacrificial layers are removed as will be discussed below, with apreferably isotropic etchant. This “release” of the micromirrors can beperformed immediately following the above-described steps, orimmediately prior to assembly with the circuitry on the secondsubstrate. If the circuitry, electrodes and micromirrors are not formedon the same substrate, then after forming the micromirrors on a lighttransmissive substrate as set forth above, a second substrate isprovided that contains a large array of electrodes on a top metal layer(e.g., metal 3) of the substrate (e.g., a silicon wafer). As can be seenin FIG. 11A, a light transmissive substrate 40 with an array ofmicromirrors 44 formed thereon as discussed above, is bonded to a secondsubstrate 60 having circuitry and electrodes at voltages V₀, V_(A) andV_(B) formed as a last layer thereon (a single electrode per micromirrorcould also be used for a micromirror embodiment with a single directionof movement such as that illustrated in FIG. 1). The micromirrors 44 arekept spaced apart from the electrodes on substrate 60 by spacers 41(e.g., photoresist spacers adjacent every micromirror and/or spacersdeposited within epoxy when bonding substrate 40 to substrate 60. One ormore electrodes on the circuit substrate electrostatically control apixel (one micromirror on the upper optically transmissive substrate) ofthe microdisplay. The voltage on each electrode on the surface of thebackplane determines whether its corresponding microdisplay pixel isoptically ‘on’ or ‘off,’ forming a visible image on the microdisplay.Details of the backplane and methods for producing apulse-width-modulated grayscale or color image are disclosed in U.S.patent application Ser. No. 09/564,069 to Richards, the subject matterof which is incorporated herein by reference. The assembly of the firstand second substrates is set forth in more detail in the Ilkov et al.patent applications referred to previously. Many different types ofwafer bonding are known in the art, such as adhesive, anodic, eutectic,fusion, microwave, solder and thermocompression bonding.

The release of the micromirrors of the present invention can be a singleor multi-step process, with the type of process depending upon the typeof sacrificial material used. In one embodiment of the invention, thefirst etch is performed that has relatively low selectivity (e.g., lessthan 200:1, preferably less than 100:1 and more preferably less than10:1), and a second etch follows that has higher selectivity (e.g.,greater than 100:1, preferably greater than 200:1 and more preferablygreater than 1000:1). Such a dual etching is set forth further in U.S.Patent Application 60/293,092 to Patel et al., filed May 22, 2001,incorporated herein by reference. Of course other release methods couldbe used, depending upon the sacrificial material. For example, if aphotoresist or other organic material is the sacrificial material,oxygen plasma ashing or a supercritical fluid release could be used.Plasmas containing pure oxygen can produce species that attack organicmaterials to form H2O, CO and CO2 as products and do not etch SiO2, Alor Si. Or, if the sacrificial material is SiO2, then an etchant such asan isotropic dry etchant (CHF3+O2, NF3 or SF6) could be used. If thesacrificial material is silicon nitride, then fluorine atoms could beused to isotropically etch the silicon nitride (e.g., CF4/O2, CHF3/O2;CH2F2 or CH3F plasmas). If the sacrificial material is amorphoussilicon, then fluorine atoms in the form of XeF2, BrF3 or BrCl3 could beused. If the sacrificial layer is aluminum, then a chlorine chemistry(BCL3, CCl4, SiCl4) could be used. Of course any etchant (andsacrificial material) would be selected at least in part based upon theamount of undercut etching needed.

Another process for forming micromirrors illustrated in FIGS. 4A to 4J.As can be seen in FIG. 4A, a substrate 30 (this can be any suitablesubstrate, such as a glass/quartz substrate or a semiconductor circuitsubstrate) that has deposited thereon a sacrificial material 31. Anysuitable sacrificial material can be used, preferably one that has alarge etching selectivity ratio between the material being etched andthe sacrificial material. One possible sacrificial material is anorganic sacrificial material, such as photoresist, or other organicmaterials such as set forth in U.S. Patent Application 60/298,529 filedJun. 15, 2001 to Reid et al. Depending upon the exact make-up of thestructural layer(s), other known MEMS sacrificial materials, such asamorphous silicon or PSG could be used. If the sacrificial material isnot directly patternable, then a photoresist layer 32 is added anddeveloped to form one or more apertures (FIG. 4B). Then, as can be seenin FIG. 4C, apertures 34 are etched into the sacrificial material 31 andthe photoresist 32 is removed. As can be seen in FIG. 4D, a (preferablyconductive) layer 35 is deposited that will ultimately form at least theflexible portions for the MEMS device (in this example a micromirrorstructure). Layer 35 can also form the posts 36 for attaching themicromirror to the substrate, or even all or part of the micromirrorbody. As will be discussed further herein, the conductive layer 35 in apreferred embodiment of the invention comprises a metal-Si,Al,B-nitride,preferably the metal is a transition metal, in particular a latetransition metal. Layer 35 could also be a plurality of (preferablyconductive) layers, or one conductive layer among many other types oflayers (structural dielectric layers, reflective layers, anti-stictionlayers, etc.). Layer 35 need not be conductive, and depending upon theexact method, target material and atmosphere used in the depositionprocess, layer 35 could also be insulating.

FIG. 4E shows the addition of photoresist 37 (patterned) followed byetching of a portion of the nitride layer(s) 35 and removal of thephotoresist (FIG. 4F). Then, as can be seen in FIG. 4G, micromirrorstructural material layer 38 is deposited. The material can beconductive or insulating, and can be a plurality of layers. If thematerial is a single layer, it is preferably reflective (e.g., analuminum or gold layer or metal alloy layer). Then, as can be seen inFIG. 4H, photoresist 39 is added and developed followed by (FIG. 4I)etching/removing portions of the layer 38 (such as in the area of theparts that will flex in operation). Finally, as can be seen in FIG. 4J,the sacrificial layer is removed to release the MEMS device so as to befree standing on the substrate. Not shown in FIG. 4 is circuitry that isformed on or in substrate 30 (if the substrate is a circuit substrate)or a light blocking layer on substrate 30 for improving automatedhandling of the substrate (if the substrate is a light transmissivesubstrate such as glass, quartz, sapphire, etc.).

As can be seen from FIGS. 4A to 4J, a free standing MEMS structure iscreated where layer 35 forms a flexible portion of the MEMS device,whereas layer 38 forms the structure that moves due to the flexiblenature of layer 35. Layer 38, as can be seen, forms both the movableportion as well as the post or wall that holds the MEMS structure on thesubstrate 30. The movable element can be formed as a laminate of layers38 and 35 (as well as additional layers if desired), or solely fromlayer 38, or even solely from layer 35. The make-up of the movable andflexible elements depend upon the ultimate stiffness or flexibilitydesired, the ultimate conductivity desired, the MEMS device beingformed, etc.

The micromirrors formed in accordance with FIGS. 1 to 4 are preferablyformed on a light transmissive substrate and have a non-deflected ‘off’state and a deflected ‘on’ state. However, the micromirrors can beformed on the same substrate as micromirror actuation circuitry andelectrodes. Also, both the ‘on’ and ‘off’ states of the micromirror canbe a position other than a flat non-deflected state. In the embodimentillustrated in FIGS. 5–9, the micromirrors are formed on the samesubstrate as electrodes and circuitry for moving the micromirrors. And,the micromirrors not only have deflected ‘on’ and ‘off’ states, but theangle of deflection is different between ‘on’ and ‘off’. As isillustrated in FIGS. 5A to 5G, a semiconductor substrate with circuitryand electrodes formed thereon (or therein) can be the starting substratefor making micromirrors in accordance with the present invention.

As can be seen in FIG. 5A, a semiconductor substrate 10 with circuitryfor controlling the micromirror, has a patterned metal layer formed intodiscrete areas 12 a to 12 e thereon—typically aluminum (e.g., the finalmetal layer in a semiconductor process). A sacrificial layer 14 isdeposited thereon, as can be seen in FIG. 5B. As in the previousembodiments, the sacrificial material can be selected from manymaterials depending upon the adjacent structures and etchant desired. Inthe present example, the sacrificial material is a novolac photoresist.As can also be seen in FIG. 5B, apertures 15 a and 15 b are formed inthe sacrificial material by standard patterning methods for a novolacphotoresist, so as to form apertures 15 a to 15 c connecting to metalareas 12 a to 12 c. After forming apertures 15 a to 15 c, as can be seenin FIG. 5C, plugs or other connections 16 a to 16 c are formed inaccordance with standard plug forming methods. For example, Tungsten (W)could be deposited by CVD by a) silicon reduction: 2WF6+3Si→2W+3SiF4(This reaction is normally produced by allowing the WF6 gas to reactwith regions of exposed solid silicon on a wafer surface at atemperature of about 300 C), b) hydrogen reduction: WF6+3H2→W+6HF (Thisprocess is carried out at reduced pressures, usually at temperaturesbelow 450 C), or c) silane reduction: 2WF6+3SiH4→2W+3SiF4+6H2 (Thisreaction (LPCVD at around 300 C) is widely used to produce a Wnucleation layer for the hydrogen reaction). Other conductive materials,particularly other refractory metals, could be used for plugs 16 a to 16c. After depositing a layer of the plug material, chemical mechanicalpolishing (CMP) is performed down to the sacrificial layer so as to formthe plugs as shown in FIG. 5C. For some plug materials, it may bedesirable to first deposit a liner in order to avoid peeling (e.g., fora tungsten plug, a TiN, TiW or TiWN liner could be deposited to surroundthe tungsten in the hole in the sacrificial material and later afterrelease of the sacrificial layer).

As can be seen in FIG. 5D, a conductive layer is deposited and patternedso as to result in discrete metal areas 18 a to 18 c, each electricallyconnected to underlying metal areas 12 a to 12 c, respectively, viaplugs 16 a to 16 c, respectively. The conductive layer can be anysuitable material (aluminum, alloys of aluminum, alloys of other metals,conductive ceramic compounds, etc.) that is deposited by suitablemethods such as physical vapor deposition or electroplating. Thematerial should preferably have both conductive properties as well as aproper combination of hardness, elasticity, etc. (as will be seen, area18 c will act as a hinge for the micromirror being formed). Of coursediscrete areas 18 a to 18 c need not be formed at the same time ifdifferent materials or properties are desired from one discrete area tothe next (likewise with the other areas formed in the device, such asareas 12 a to 12 e and plugs 18 a to 18 c). Naturally fewer processsteps are involved if each discrete area within a layer is of the samematerial deposited at the same time. In a preferred embodiment, thisconductive layer is either an aluminum alloy or a conductive binary orternary (or higher) compound such as those disclosed in U.S. patentapplication Ser. No. 60/228,007 to Reid filed Aug. 23, 2000 and U.S.Patent Application 60/300,533 to Reid filed Jun. 22, 2001, bothincorporated herein by reference, deposited by reactive sputtering. Theappropriate etching chemistry is used to pattern the conductive layer(e.g., a chlorine chemistry for aluminum) so as to form discreteconductive areas 18 a to 18 c.

As further illustrated in FIG. 5E, a second layer of sacrificial layer20 is deposited that could be the same or different from the sacrificialmaterial of layer 14 (preferably the material is the same so that bothlayers can be removed simultaneously). Then, layer 20 is patterned so asto form aperture 20 a down to area 18 c. As with forming apertures insacrificial layer 14, this can be done with an additional layer ofphotoresist or layer 20 can be directly patterned if the material is aphotoresist or other directly patternable material. As can be seen inFIG. 5F a plug or connection 22 is formed by depositing a preferablyelectrically conductive material on sacrificial layer 20, followed bychemical mechanical polishing, leaving plug 22 connected to discretearea (“hinge”) 18 c. Then, as can be seen in FIG. 5G, micromirror body24 is formed by depositing a (preferably conductive) layer followed bypatterning into the desired shape of the micromirror. Many micromirrorshapes are possible, such as that illustrated in FIG. 6A, and as will bediscussed in further detail herein. However, the micromirror shape inaccordance with this example of the invention can have any shape,including square or diamond as shown in FIGS. 6B and 6C. Of course,those shapes that allow for tight packing of micromirrors and thus ahigh fill factor are preferred (such as the shape of the micromirror inFIG. 6A illustrated in a close fitting array in FIG. 7). Dotted line 62in FIG. 6C (and later in FIG. 12) is the axis or rotation of themicromirror.

For various layers used in making the micromirror in accordance withFIGS. 5A to 5G are illustrated as single layers, however, each layer(whether structural or sacrificial) could be provided as a laminatee.g., one layer of the laminate having improved mechanical performanceand another layer having improved conductivity. Also, though in thepreferred embodiment the structural materials are conductive, it ispossible to make micromirror element 24 (or a layer within a laminate24) conductive, as well as actuation electrodes 12 d and 18 b (andlayers/materials connecting electrodes 12 d and 18 b to thesemiconductor substrate). Furthermore, the materials disclosed above(metal, metal alloys, metal-ceramic alloys, etc.) need not contain anymetal, but could, for example be silicon (e.g., polycrystalline silicon)or a compound of silicon (e.g., Si3N4, SiC, SiO2, etc.). If Si3N4 isused as a structural material and amorphous silicon is used as thesacrificial material, xenon difluoride could be utilized as a gas phaseetchant in order to remove the sacrificial amorphous silicon. Ifdesired, the silicon or silicon compound (or other compound) used as astructural material could be annealed before and/or after removing thesacrificial layer to improve the stress characteristics of thestructural layer(s). FIG. 8 is an exploded view of the micromirrorformed in accordance with FIGS. 5A to 5G.

One of the final steps in making the micromirror is removing sacrificiallayers 14 and 20. FIG. 9A is an illustration of the micromirror afterremoval of the two sacrificial layers, showing micromirror 24 connectedto substrate 10 via post 22, hinge 18 c, post 16 c and metal areas 12 c.The micromirror as shown in FIG. 9A is not moved or deflected, as novoltages are applied to any underlying electrodes (discrete metal areasformed in the above-described process) e.g., electrodes 18 b or 12 d.This non-deflected position is not the ‘off’ position for themicromirror, which for projection systems is generally the furthestangle away from the ‘on’ position (in order to achieve the best contrastratio for the projected image). The ‘on’ state of the micromirror, thatis, the position of the micromirror that deflects light into theacceptance cone of the collection optics, is illustrated in FIG. 9B. Avoltage V_(A) is applied to electrode 12 d in order to electrostaticallypull down micromirror plate 24 until the edge of plate 24 impactselectrode 12 e. Both micromirror plate 24 and electrode 12 e are at thesame potential, in this example at a voltage of V₀. As illustrated inFIG. 9C, when a voltage V_(B) is applied to electrode 18 b, micromirrorplate 24 deflects in an opposite direction, with its movement beingstopped by electrode 18 a. Both electrode 18 a and micromirror plate 24are at the same potential (in this example a V₀ voltage). Depending uponthe size of electrode 18 b vs. electrode 12 d, and the distance betweenthese electrodes and the micromirror plate 24, the voltages applied toelectrodes 18 b and 12 d need not be the same. This deflected positionillustrated in FIG. 9C is the ‘off’ position, and deflects lightfurthest away from the collection optics.

As can be seen by comparing FIGS. 9B and 9C, the off position forms alower angle (with the substrate) than the on position. Hereafter, whenreferring to the on and off angles (or such angles relative to thesubstrate or a non-deflected micromirror position), a sign of the anglewill be used (positive or negative relative to the substrate ornon-deflected position). The sign is arbitrary, but signifies that themicromirrors rotate in one direction to an ‘on’ position and in anopposite direction to an ‘off’ position. The benefits of such asymmetrywill be discussed in further detail below. In one example of theinvention, the on position is from 0 to +30 degrees and the off positionis from 0 to −30, with movement to the on position being greater thanmovement to the off position. For example, the on position could be from+10 to +30 degrees (or +12 to +20 degrees or +10 to +15 degrees) and theoff position could be greater than 0 and between 0 and −30 degrees (orwithin a smaller range of between 0 and −10 or −12, or from −1 to −12,or −1 to −10 or −11 degrees, or −2 to −7 degrees). In another example,the micromirrors are capable of rotating at least +12 degrees to the onposition and between −4 and −10 degrees to the off position. Dependingupon the materials used for the hinges, greater angles could be usedachieved, such as an on rotation from +10 to +35 degrees and an offrotation from −2 to −25 degrees (of course materials fatigue and creepcan become an issue at very large angles). Not taking into account thedirection of rotation, it is preferred that the on and off positions areat angles greater than 3 degrees but less than 30 degrees relative tothe substrate, preferably the on position is greater than +10 degrees,and that the mirrors rotate 1 degree (or more) further in the ondirection than in the opposite off direction.

FIGS. 10A to 10D illustrate a further method and micromirror structure.Variability in materials, layers, sacrificial etching, depositing ofstructural layers, etc. are as above with respect to the previouslydescribed processes. For the method illustrated in FIGS. 10A to 10D, thesubstrate 40 could be either a light transmissive substrate (to later bejoined to a second substrate with circuitry and electrodes) or asemiconductor substrate already having circuitry and electrodes thereon.In the present example as will be seen in FIGS. 11A to 11B, thecircuitry and electrodes are formed on a separate substrate.

In FIG. 10A, a sacrificial layer 42 is deposited and patterned so as toform aperture 43. Then, as illustrated in FIG. 10B, plug 46 is formed(preferably as in the process of FIG. 5A to 5G—deposit a metal, metalalloy or other conductive layer and planarize (e.g., by CMP) to form theplug). Then, as can be seen in FIG. 10C, a hinge 50 is formed bydepositing an electrically conductive material (having suitableamorphousness, elasticity, hardness, strength, etc.). In the presentexample, the hinge (and/or micromirror) is an early transition metalsilicon nitride such as Ta—Si—N, a late transition metal silicon nitridesuch as Co—Si—N or a metal or metalceramic alloy such as a titaniumaluminum alloy, or a titanium aluminum oxide alloy. After depositingsuch a material, a photoresist is deposited and patterned so as to allowfor etching/removal of all areas except for the hinge areas 50. Then, ascan be seen in FIG. 10D, micromirror plate 44 is formed by firstprotecting the hinges with photoresist and then depositing andpatterning a hinge structure layer so as to form micromirror plate 44partially overlapping and therefore connecting with hinge 50. As in theother embodiments, an array of thousands or millions of suchmicromirrors is formed at the same time in an array.

Then, whether at the wafer or die level, the substrate with micromirrorsis attached to a substrate with actuation circuitry and electrodes.There should be at least two electrodes per micromirror in the presentexample, one for each direction of deflection, and preferably a thirdfor allowing the micromirror to stop movement (in one of the directions)by hitting a material at the same potential as the micromirror itself.The second substrate 60 with electrodes 72 and 74 for deflecting themicromirror, and a landing pad or electrode 70, is illustrated in FIG.11A. The micromirror is in a non-deflected position in FIG. 11A. When avoltage V_(A) is applied to electrode 72, micromirror 44 is deflecteduntil it impacts electrode 70 (FIG. 11B). This is the ‘on’ position ofthe micromirror that allows light to enter into the collection optics ofthe system. It is possible to design the gap between the substrates sothat the ends of micromirror plate 44 impact electrode 70 and substrate40 at the same time. When a voltage V_(B) is applied to electrode 74,micromirror plate 44 deflects in the opposite direction until the end ofthe micromirror impacts substrate 40. This is the ‘off’ position of themicromirror (FIG. 11C). Due to the position of the hinge 50 and post 46,the angle of the micromirror in this ‘off’ position is less than theangle of the micromirror in the ‘on’ position. An array of suchmicromirrors is illustrated in FIG. 12, and an exploded view of amicromirror made in accordance with the process of FIGS. 10A to 10D isshown in FIG. 13.

FIG. 14A is a cross sectional view of multiple micromirrors within anarray where micromirrors in their ‘off’ state are not deflected (group100) whereas micromirrors in their ‘on’ state (group 102) are moved fromthe flat state so as to project light where the light can be viewed(directly, on a target within a unitary device, across a room onto ascreen, etc.). Such a micromirror array arrangement is betterillustrated in FIGS. 14B and 14C. As can be seen in FIG. 14B, in themicromirrors' ‘on’ state, an incoming cone of light 50 is reflected offof the micromirrors (all micromirrors are ‘on’ in this figure) and lightis projected away as a cone of light 52 into output aperture 60, and inmost cases will proceed to an imaging system (e.g., a projection lens orlenses). Cone 54 represents specular reflection from the transparentcover. FIG. 14C is an illustration of the micromirrors in their ‘off’state, where cone 52 represents light reflected from the micromirrors inthis ‘off’ state. The incident and reflected cones of light will narrowonto the entire array, though in these figures, for ease ofillustration, the cones of light are shown as tapering onto anindividual micromirror.

The arrangement of FIGS. 14B and 14C has the benefit that when themicromirrors are in their ‘off’ (non-deflected) state, little light isable to travel through the gaps between the micromirrors and causeundesirable “gap scatter”. However, as shown in FIG. 14C, diffractedlight is caused by the repeating pattern of the micromirrors (light 61 aand 61 b that extends beyond the cone of reflected ‘off’ light 52). Thisundesirable light is caused by scattering or diffraction from the edgesof the micromirrors (“edge scatter”). In particular, because theincoming cone of light (and thus the outgoing cones of light) is made aslarge as possible so as to increase efficiency, diffraction light suchas light 61 a that extends beyond the cone of reflected ‘off’ light canenter the output aperture 60 (e.g., collection optics) and undesirablydecrease contrast ratio.

In order to avoid this “overlap” of ‘off’ state light (includingdiffraction light) and ‘on’ state light that decreases contrast ratio,the ‘off’ state light and ‘on’ state light can be separated further fromeach other by deflecting micromirrors for both the ‘on’ and ‘off’states. As can be seen in FIG. 15A, if the micromirror is deflected inits ‘off’ state as illustrated in this figure, some light will beproperly reflected off of the micromirrors far away from the ‘on’ statedirection (e.g., collection optics) as shown as ray 116. Other light 112will not hit on a micromirror, but will scatter on the top surface ofthe lower substrate (e.g., on lower circuitry and electrodes) and enterinto the collection optics even though the adjacent micromirror is inthe ‘off’ state. Or, as can be seen by ray 114, the incoming light couldhit a micromirror, yet still result in gap scatter rather than beingproperly directed in the ‘off’ angle like ray 116. This ‘on’ arrangementas illustrated in FIG. 15B is the same as in FIG. 14B. However, asillustrated in FIG. 15C, the ‘off’ state along with diffraction 61 acaused by micromirror periodicity, is moved further away from the ‘on’angle so as to result in improved contrast ratio due to diffraction/edgescatter (though decreased contrast ratio due to gap scatter, asmentioned above).

An improved micromirror array would maximize the distance between the‘off’ light cone and the ‘on’ light cone (minimize edge scatter into theacceptance cone), yet minimize gaps between adjacent micromirrors(minimize gap scatter). One solution that has been tried has been toprovide a micromirror array with micromirrors that deflect in oppositedirections for the ‘on’ and ‘off’ states as in FIGS. 15A to 15C, andprovide a light absorbing layer under the micromirrors so as to decreasegap scatter. Unfortunately, this increases process complexity, orabsorbs light onto the micromirror array assembly (onto the lightvalve), which increases the temperature of the light valve and causesproblems due to thermal expansion, increased fatigue or droop ofmicromirror structures, increased breakdown of passivation films, selfassembled monolayers and/or lubricants, etc.

As can be seen in FIGS. 16A to 16C micromirrors are provided that aredeflected in both their ‘on’ and ‘off’ states, yet at differentdeflection angles. As can be seen in FIG. 16A micromirrors 100 aredeflected in an ‘off’ state that is at a deflection angle less thanmicromirrors 102 in their ‘on’ state (deflected in an opposite directionfrom the flat or nondeflected position). As can be seen in FIG. 16B, the‘on’ state is unchanged (incoming light 50 projected as outgoing light52 into output aperture 60), with some specular reflection 54. In FIG.16C, micromirrors are in their ‘off’ state in a sufficiently deflectedposition such that edge scattering light 61 a that passes into outputaperture 60 is minimized, yet deflected only so much as to keep suchedge scattering light out of the acceptance cone so as to minimize gapscattering light from under the micromirrors due to a large off statedeflection angle.

An additional feature of the invention is in the packaging of thedevice. As mentioned above, reflection off of the light transmissivesubstrate can result in specular reflection. As can be seen in FIG. 17A,incoming light cone 50 reflects off of micromirrors in their onposition, illustrated as reflected cone 52. Specular light reflectedfrom a surface of the light transmissive substrate 32 is illustrated aslight cone 54. It is desirable in making a projection system, toincrease the distended angle of the cone so as to increase etendue andprojection system efficiency. However, as can be seen in FIG. 17A,increasing the distended angle of cone 50 will result in increases inthe distended angles of cones 52 and 54 such that specular reflectionlight from cone 54 will enter the output aperture 60, even if themicromirrors are in their ‘off’ state (thus reducing contrast ratio).

In order to allow for larger distended angles of cones of light yetavoid specular reflection entering the output aperture, as can be seenin FIG. 17B, light transmissive substrate 32 is placed at an anglerelative to substrate 30. In many cases, substrate 30 is the substrateupon which the micromirrors (or other optical MEMS elements) are formed,whereas substrate 32 is a light transmissive window in a package for theoptical MEMS device. The angle of the window is greater than −1 degree(the minus sign in keeping with the directions of the angles or themicromirrors). In one example, the window is at an angle of from −2 to−15 degrees, or in the range of from −3 to −10 degrees. In any event,the window is at an angle relative to the micromirror substrate that ispreferably in the same “direction” as the off position of themicromirrors (relative to the micromirror substrate and/or packagebottom). As can be seen in FIG. 17B, when the micromirrors are in the‘on’ state, there is a gap between the light reflected as light from‘on’ micromirrors (light reflectance cone 52) and specular reflectionlight (light cone 54). This “gap” is due to specular reflection cone 54being reflected at a greater distance due to the angled lighttransparent substrate. This arrangement allows, as can be seen in FIG.17C, for increasing the distended angle of the incident light cone (andthe corresponding reflectance light cones) from the ‘on’ micromirrors(cone 52) and the light transparent substrate (cone 54). (For ease ofillustration, the reflectance point of the light cones is midway betweenthe micromirror and the light transmissive substrate, though in realitylight cone 52 reflects from the micromirror(s) and specular reflectioncone 54 reflects from the substrate 32.) The angled light transmissivewindow as illustrated in FIGS. 17B and 17C allow for larger throughput,greater system efficiency, greater light value etendue (etendue=solidangle times area). A light valve such as illustrated in FIGS. 17B and17C is capable of modulating a larger etendue light beam and can passthrough more light from a light source and is thus more efficient).

A packaged device is illustrated in FIGS. 17D and 17E. As can be seen inFIG. 17D, incoming light 40 (this view is reversed from previous views)is incident on the array and reflected therefrom. As can be seen in FIG.17E, an angled light transmissive substrate 32 (with mask areas 34 a and34 b) not only allows for increased light cone distended angles as notedabove, but in addition a gap between the mask of window 32 and themicromirror array is minimized, thus reducing light scattering andtemperature build-up in the package. The angle of the light transmissivewindow is from 1 to 15 degrees relative to the substrate, preferablyfrom 2 to 15 degrees, or even from 3 to 10 degrees. As can be seen inFIGS. 17D to 17E, bond wires 37 at one end of the substrate in thepackage (electrically connecting the substrate to the package foractuation of the micromirrors—or other micromechanical element) aredisposed where the angled window is at a greater distance than at anopposite end of the substrate. Thus, the angled window allows for thepresence of bond wires, yet allows for a minimized distance between thelight transmissive window and the micromirror substrate at an end of thesubstrate where there are no bond wires. Note that light is incident onthe micromirror array from a side of the package corresponding to theposition of the bond wires and elevated side of the angled window.Additional components that could be present in the package are packageadhesives, molecular scavengers or other getters, a source of stictionreducing agent (e.g. chlorosilanes, perfluorinated n-alkanoic acids,hexamethyldisilazane, etc.).

If the micromirrors of the present invention are for a projectiondisplay, there should be a suitable light source that illuminates thearray and projects the image via collection optics to a target. Thearrangement of light source and incident light beam to the array, and toeach micromirror, which allows for the improved contrast ratio whileminimizing projection system footprint, in the present invention, can beseen in FIGS. 18 and 19 a to 19 c. As can be seen in FIG. 18, a lightsource 114 directs a beam of light 116 at a 90 degree angle to theleading side 93 of the active area of the array (the active area of thearray illustrated as rectangle 94 in the figure). The active area 94would typically have from 64,000 to about 2,000,000 pixels in a usuallyrectangular array such as illustrated in FIG. 18. The active area 94reflects light (via ‘on’ state micromirrors) through collection optics115 to a target to form a corresponding rectangular image on the target(e.g., wall or screen). Of course, the array could be a shape other thanrectangular and would result in a corresponding shape on the target(unless passed through a mask). Light from light source 114 reflects offof particular micromirrors (those in the ‘on’ state) in the array, andpasses through optics 115 (simplified as two lenses for clarity).Micromirrors in their ‘off’ state (in a non-deflected “rest” state),direct light to area 99 in FIG. 18. FIG. 18 is a simplification of aprojection system that could have additional components such as TIRprisms, additional focusing or magnification lenses, a color wheel forproviding a color image, a light pipe, etc. as are known in the art. Ofcourse, if the projection system is for maskless lithography ornon-color applications other than one for projection of a color image(e.g. front or rear screen projection TV, a computer monitor, etc.),then a color wheel and different collection optics could be used. And, atarget may not be a screen or photoresist, but could be a viewer'sretina as for a direct view display. As can be seen in FIG. 18, all ‘on’micromirrors in the array direct light together to a single collectionoptic, which can be one lens or a group of lenses fordirecting/focusing/projecting the light to a target.

Whether the viewed image is on a computer, television or movie screen,the pixels on the screen image (each pixel on the viewed or projectedimage corresponding to a micromirror element in the array) have sidesthat are not parallel to at least two of the four sides defining therectangular screen image. As can be seen in one example of a micromirrorelement in FIGS. 19A–E, the incident light beam does not impingeperpendicularly on any sides of the micromirror element. FIG. 19A is aperspective view of light hitting a single micromirror element, whereasFIG. 19B is a top view and FIG. 19C is a side view. The incident lightbeam may be from 10 to 50 degrees (e.g., 20 degrees) from normal (to themicromirror/array plane). See angle 133 in FIG. 19C.

Regardless of the angle of the incident light beam from the plane of themicromirror, no micromirror sides will be perpendicular to the lightbeam incident thereon (see FIG. 19D). In a preferred embodiment, themicromirror sides should be disposed at an angle (131) less than 80degrees or preferably 55 degree or less in relation to the incidentlight beam axis projection on the micromirror plane (102), morepreferably 45 degrees or less, and most preferably 40 degrees or less.Conversely, angle 132 should be 100 degrees or more, preferably 125degrees or more, more preferably 135 degrees or more, and mostpreferably 140 degrees or more. The switching (i.e., rotational) axis ofthe micromirror is labeled as dotted line 103 in FIG. 19D. Thisswitching axis could be in other places along the micromirror, e.g.,line 106, depending upon the type of hinges utilized. As can be seen inFIG. 19D, the switching axis (e.g., 103 or 106) is perpendicular to theincident light beam 102 as projected onto the plane of the micromirror.FIG. 19E, like 19D, is a top view—however an array of micromirrors areillustrated in FIG. 19E along with an incident light beam 102 onto the2-D array of micromirrors. Note that each micromirror in FIG. 19E hasthe shape of the micromirror illustrated in FIGS. 19A–D. As can be seenin FIG. 19E, the overall shape of the micromirror array is a rectangle.Each of the four sides of the array, 117–120, is defined by drawing aline between the most remote pixels in the last row and column of theactive area (121–124) (e.g., side 119 being defined by a lineintersecting corner pixels 123 and 122). Though it can be seen in FIG.19E that each of the “leading” (closest to the light source) and“trailing” (furthest from the light source) active area sides 119, 117is “jagged” due to the shape of the micromirrors in the active area, itshould be remembered that there could be up to about 3,000,000micromirrors or more in an area of from 1 cm² to 1 in². Therefore,unless under extreme magnification, the active area will be essentiallyrectangular, with active area sides 118 and 120 (or 117 and 119)parallel to micromirror sides 107 and 108 in FIG. 19D (the micromirrorin FIG. 19D being one of the micromirror elements within the active areaof FIG. 19E); with active area sides 117 and 119 (or 118 and 120) beingparallel to the switching axis 103 (or 106) of each micromirror (seeFIG. 19D); and with active area sides 117 and 119 (or 118 and 120) beingnon-perpendicular to leading or trailing sides 125 a–d of themicromirrors (see FIG. 19D). FIG. 19E could also be seen as theprojected image comprising a large number of projected pixels (eachprojected pixel having the shape illustrated in FIG. 19D). In accordancewith the above, therefore, the projected image sides 118 and 120 (or 117and 119) are parallel to projected pixel sides 107 and 108, andprojected image sides 117 and 119 (or 118 and 120) beingnon-perpendicular to projected pixel sides 125 a–d.

FIG. 20 is an illustration of a 2-D micromirror array (of course withmany fewer pixels than within the typical active area). For ease ofillustration (in FIG. 20 as well as FIGS. 21–26 and 29–32) fewer than 60micromirrors/pixels are illustrated, though a typical display would havefrom 64K pixels (320×200 pixels) to 1,920K pixels (1600×1200pixels=UXGA), or higher (e.g., 1920×1080=HDTV; 2048×1536=QXGA). Due tothe very small size of each pixel in the present invention, theresolution that can be achieved is essentially without limit. As can beseen in FIG. 20, the sides of each pixel are parallel to correspondingsides of the active area. Thus, each micromirror side is eitherperpendicular or parallel to the sides of the active area. In contrast,as illustrated in FIG. 21, the micromirror sides are neither parallelnor perpendicular to the active area sides. As will be seen below, inother embodiments, some of the sides are neither parallel norperpendicular to active area sides, and some sides can be parallel toactive area sides (as long as also parallel to the direction of a linesuperimposed on the plane of the micromirror from the incident lightbeam).

The micromirror array as illustrated in FIG. 22 achieves high contrastratio. However, the micromirror arrangements such as illustrated inFIGS. 23–29 simplify the addressing scheme. More particularly, FIGS.23–29 have the advantage of not positioning the pixels on a latticealigned at an angle to the X and Y axes of the array. As typical videoimage sources provide pixel color data in an X-Y grid, the arrangementof pixels in FIGS. 23–29 avoids non-trivial video preprocessing torender an acceptable image on a display. Also the arrangement of FIGS.23–29 avoids a more complicated layout of the display backplane (inrelation to FIGS. 13 and 14, which could require twice as many row orcolumn wires to the pixel controller cells). Horizontal line 80 in FIG.22 connects the top row of micromirror elements, and vertical lines81A–D extend from each of these top row micromirrors (these horizontaland vertical lines corresponding to addressing rows and columns in thearray. As can be seen in FIG. 22, only every other micromirror isconnected in this way. Thus, in order for all micromirrors to beaddressed, twice as many rows and columns are needed, thus resulting inadded complexity in addressing the array. FIG. 22 also shows supportposts 83 at the corners of the micromirrors that support posts connectto hinges (not shown) below each micromirror element (the “superimposedhinges” discussed hereinabove) and to an optically transmissivesubstrate (not shown) above the micromirror elements.

In a more preferred embodiment of the invention as shown in FIG. 23, anarray 92 is provided. A light beam 90 is directed at the array such thatno micromirror sides are perpendicular to the incident light beam. InFIG. 23, the leading sides of the micromirrors (relative to incidentlight beam 90) are at an angle of about 135 degrees to the incidentlight beam (90). It is preferred that this angle be greater than 100degrees, preferably greater than 130 degrees. The contrast ratio isfurther improved if the angle between the incident light beam and theleading side is 135 degrees or more, and can even be 140 degrees ormore. As can be seen in FIG. 23, the micromirror elements' orientationdoes not result in addressing issues as discussed above with respect toFIG. 22. Posts 95 connect to hinges (not shown) below each micromirrorelement in FIG. 23. The hinges extend perpendicularly to the directionof the incident light beam (and parallel to the leading and trailingsides 91B and 91D of the active areas). The hinges allow for an axis ofrotation of the micromirrors that is perpendicular to the incident lightbeam.

FIG. 24 is an illustration of micromirrors similar to that shown in FIG.23. In FIG. 24, however, the micromirror elements are “reversed” andhave their “concave” portion as their leading side. Even though themicromirrors in FIG. 24 are reversed from that shown in FIG. 23, thereare still no sides of the micromirrors that are perpendicular to theincident light beam. FIG. 24 illustrates a hinge 101 disposed in thesame plane as the micromirror element to which the hinge is attached.Both types of hinges are disclosed in the '840 patent mentioned above.FIG. 25 likewise illustrates a hinge 110 in the same plane as themicromirror array, and shows both “convex” portions 112 (“protrusions”)and “concave” portions 113 (“cut-outs”) on the leading side of eachmicromirror. Due to the concave or cut-out portion of each micromirror,each micromirror is in a shape of a concave polygon. Though themicromirrors can be convex polygons (if no sides of the convex polygonalmicromirrors are parallel to the leading side of the active area), it ispreferred that the micromirrors have a concave polygon shape. Convexpolygons are known as polygons where no line containing a side can gothrough the interior of the polygon. A polygon is concave if and only ifit is not a convex polygon. The concave polygon shape can be in the formof a series of (non-rectangular) parallelograms, or with at least oneconcave and a matching at least one convex portion (for fitting withinthe concave portion of the adjacent micromirror), though any concavepolygon shape is possible. Though less preferred, as mentioned above,the micromirror shape could also be that of a single (non-rectangular)parallelogram. Though not illustrated, the matching one or moreprotrusions and one or more cut-outs need not be composed of straightlines (nor any of the micromirror sides for that matter), but insteadcould be curved. In one such embodiment, the protrusion(s) andcut-out(s) are semicircular, though the illustrated angular protrusionsand cut-outs are preferred.

FIGS. 26A to 26F illustrate further embodiments of the invention. Thoughthe shape of the micromirrors are different in each figure, each is thesame in that none has any sides perpendicular to the incident lightbeam. Of course, when a micromirror side changes direction, there is apoint, however small, where the side could be considered perpendicular,if only instantaneously. However, when it is stated that there are nosides perpendicular, it is meant that there are no substantial portionswhich are perpendicular, or at least no such substantial portions on theleading side and trailing side of the micromirrors. Even if thedirection of the leading sides changed gradually (or a portion of theleading side is perpendicular to the incident light beam, such asillustrated in FIG. 29), it is preferred that there would never be morethan ½ of the leading side that is perpendicular to the incident lightbeam, more preferably no more than ¼, and most preferably 1/10 or less.The lower the portion of the leading side and trailing side that isperpendicular to the incident light beam, the greater the improvement incontrast ratio.

Many of the micromirror embodiments can be viewed as an assembly of oneor more parallelograms (e.g., identical parallelograms). As can be seenin FIG. 27A, a single parallelogram is effective for decreasing lightdiffraction as it has no sides perpendicular to the incident light beam(the light beam having a direction from the bottom to the top of thepage and starting from out of the plane of the page). FIG. 27Aillustrates a single parallelogram with a horizontal arrow indicatingwidth “d” of the parallelogram. The switching axis for the micromirrorin FIG. 27A (and FIGS. 27B to 27F) is also in this horizontal direction.For example, the switching axis could be along the dotted line in FIG.27A. FIGS. 27B and 27C show both two and three parallelogram micromirrordesigns, where each subsequent parallelogram has the same shape, sizeand appearance as the one before. This arrangement forms a “saw-tooth”leading and trailing side of the micromirror element. FIGS. 27D to 27Fillustrate from 2 to 4 parallelograms. However, in FIGS. 27D to 27F,each subsequent parallelogram is a micromirror image of the one before,rather than the same image. This arrangement forms a “jagged side” onthe leading and trailing sides of the micromirror elements. It should benoted that the parallelograms need not each be of the same width, and aline connecting the tips of the saw-tooth or jagged sides need not beperpendicular to the incident light beam. The width of eachparallelogram, if they are constructed to be of the same width, will be“d”=M/N, where M is total micromirror width, N is the number ofparallelograms. With an increasing number of parallelograms, the width“d” is decreasing (assuming constant micromirror width). However, width“d” should preferably be much larger than the wavelength of the incidentlight. In order to keep the contrast ratio high, the number ofparallelograms N (or the number of times the leading micromirror sidechanges direction) should be less than or equal to 0.5 M/λ, orpreferably less than or equal to 0.2 M/λ, and even less than or equal to0.1 M/λ, where λ is the wavelength of the incident light. Though thenumber of parallelograms is anywhere from 1 to 4 in FIG. 27, any numberis possible, though 15 or fewer, and preferably 10 or fewer result inbetter contrast ratio. The numbers of parallelograms in FIG. 27 are mostpreferred (4 or fewer).

As can be seen in FIG. 28, hinges (or flexures) 191, 193 are disposed inthe same plane as micromirror element 190. Incident light beam 195 froma light source out of the plane of FIG. 28 impinges on leading sides ofmicromirror 190, none of which are perpendicular. It is preferred thatno portion of the hinges be perpendicular to the incident light beam, soas to decrease light diffraction in direction of micromirror switching.

Also, it should be noted that the “straight” micromirror sides that areillustrated as being parallel to active area sides (e.g., micromirrorsides 194, 196 in FIG. 28) can have other shapes as well. FIG. 21 aboveis one example where there are no micromirror sides parallel to incidentlight beam 85. FIGS. 30 and 31 are further examples where no micromirrorsides are perpendicular or parallel to the incident light beam, yet donot have the increased addressing complexity as that of FIG. 22.Incident light can be directed substantially perpendicularly to any ofthe four active area sides in FIG. 30 (see arrows 1–4) and not beincident perpendicularly on any micromirror sides. This unique featureis also present in the array illustrated in FIG. 31. It is also possibleto have part of the leading edge of each micromirror perpendicular tothe incident light beam and part not perpendicular as can be seen inFIG. 29.

FIGS. 32A to 32J illustrate possible hinges for the micromirrors of thepresent invention. Similar to FIG. 24, FIG. 32A illustrates micromirrorswith flexures 96 extending parallel to the incident light beam (whenviewed as a top view as in this figure) and connecting micromirror 97 tosupport post 98 which holds the micromirror element on the substrate.Incident light could be directed at the array in the direction of arrows5 or 6 in FIG. 32A (as viewed from above). Of course the incident lightwould originate out of plane (see FIGS. 11A to 11E). Such incident lightwould be the same for FIGS. 32B to 32L. FIGS. 32C to 32E are furtherembodiments of this type of hinge. FIGS. 32F to 32L are illustrations offurther hinge and micromirror embodiments where, except for FIG. 32J,the hinges do not extend parallel to the incident light beam (or leadingactive area side) and yet can still result in the micromirrors rotatingaround an axis of rotation perpendicular to the incident light beam.

When micromirror sides that are parallel to the rotation axis of themicromirror (and perpendicular to the incident light beam) are notminimized, light diffracted by such micromirror sides, will pass throughthe collection optics even if the micromirror is in ‘off’ state, thusreducing the contrast ratio. As can be seen in FIG. 33A, a diffractionpattern (caused by illuminating an array of substantially squaremicromirrors such as that of FIG. 20 at an angle of 90 degree to theleading side of the array) in the shape of a “+” intersects theacceptance cone (the circle in the figure). The diffraction pattern canbe seen in this figure as a series of dark dots (with a correspondinglighter background) that form one vertical and one horizontal line, andwhich cross just below the acceptance cone circle shown as a circularsolid black line superposed onto the diffraction pattern). Though notshown, in the micromirror's ‘on’ state, the two diffraction lines wouldcross within the acceptance cone circle. Therefore, as can be seen inFIG. 33A, the vertical diffraction line will enter the acceptance coneof the collection optics even when the micromirror is in the ‘off’state, thus harming the contrast ratio. FIG. 33B is a diffractionpattern caused by illuminating an array of square micromirrors at a 45degree angle. As can be seen in FIG. 33B, diffraction light passing intothe acceptance cone (the small solid black circle in FIG. 33B) isreduced compared to FIG. 33A. However, as mentioned above, thoughdiffraction can be reduced by such an illumination, other problemsarise.

In contrast, as can be seen in FIG. 33C, the diffraction pattern of thepresent invention (micromirror from FIG. 28 in ‘off’ state) does nothave a diffraction line extending though the collection opticsacceptance cone, or otherwise to the spatial region where light isdirected when the micromirror is in the ‘on’ state. Thus substantiallyno diffracted light is passed to the area where light is passed when themicromirror is in the ‘on’ state. A micromirror array producing such adiffraction pattern, with illumination light orthogonal to the sides ofthe active area of the array (and/or orthogonal to the columns or rows)is new. Likewise, the micromirror designs, hinges therefore, andarrangement of light source to the micromirrors, active area sidesand/or addressing rows and columns are also new.

The invention has been described in terms of specific embodiments.Nevertheless, persons familiar with the field will appreciate that manyvariations exist in light of the embodiments described herein. Forexample, the micromirror shapes of the present invention could be usedfor micromirrors in an optical switch (e.g., such as disclosed in U.S.patent application Ser. No. 09/617,149 to Huibers et al. filed Jul. 17,2000, and U.S. Provisional Patent Application No. 60/231,041 to Huibersfiled Sep. 8, 2000, both incorporated herein by reference) in order todecrease diffraction in the switch. In addition, the micromirrors of thepresent invention can be made in accordance with structures and methods,such as those set forth in U.S. patent application Ser. No. 09/767,632to True et al. filed Jan. 22, 2001, U.S. patent application Ser. No.09/631,536 to Huibers et al. filed Aug. 3, 2000, U.S. patent applicationSer. No. 60/293,092 to Patel et al. filed May 22, 2001, and U.S. patentapplication Ser. No. 06/637,479 to Huibers et al. filed Aug. 11, 2000.Also, though a standard red/green/blue or red/green/blue/white colorwheel could be used in a projection display incorporating themicromirrors of the present invention, other color wheels could be used,such as disclosed in U.S. Provisional Patent Application No. 60/267,648to Huibers filed Feb. 9, 2001 and Ser. No. 60/266,780 to Richards et al.filed Feb. 6, 2001, both incorporated herein by reference.

Also, the present invention is suited for a method utilizing a removable(and replaceable) substrate for singulation and assembly purposes suchas set forth in U.S. Provisional Patent Application No. 60/276,222 toPatel et al. filed Mar. 15, 2001. In addition, the micromirrors of thepresent invention can be actuated within an array by pulse widthmodulation such as set forth in U.S. patent application Ser. No.09/564,069 to Richards, filed May 3, 2000, the subject matter of whichbeing incorporated herein by reference. Furthermore, if interhalogens ornoble gas fluorides are used as etchants for the release of themicromirrors, methods could be used such as set forth in U.S. patentapplication Ser. No. 09/427,841 to Patel et al. filed Dec. 26, 1999 andSer. No. 09/649,569 to Patel et al. filed Aug. 28, 2000, both beingincorporated herein by reference. Or, the sacrificial materials and themethods for removing them could be those set forth in U.S. PatentApplication 60/298,529 to Reid et al. filed Jun. 15, 2001. In addition,other structural materials could be used, such as the MEMS materials setforth in U.S. patent application 60/228,007 filed Aug. 23, 2000 and U.S.patent application Ser. No. 60/300,533 filed Jun. 22, 2001. Each of theabove patents and applications are incorporated herein by reference.

Throughout the present application structures or layers are disclosed asbeing “on” (or deposited on), or over, above, adjacent, etc. otherstructures or layers. It should be recognized that this is meant to meandirectly or indirectly on, over, above, adjacent, etc., as it will berecognized in the art that a variety of intermediate layers orstructures could be interposed, including but not limited to sealantlayers, adhesion promotion layers, electrically conductive layers,layers for reducing stiction, etc. In the same way, structures such assubstrate or layer can be as a laminate due to additional structures orlayers. Also, when the phrase “at least one” or “one or more” (orsimilar) is used, it is for emphasizing the potential plural nature ofthat particular structure or layer, however this phraseology should inno way imply the lack of potential plurality of other structures orlayers that are not set forth in this way. In the same way, when thephrase “directly or indirectly” is used, it should in no way restrict,in places where this phrase is not used, the meaning elsewhere to eitherdirectly or indirectly. Also, “MEMS”, “micromechanical” and “microelectromechanical” are used interchangeably herein and the structure mayor may not have an electrical component. Lastly, unless the word “means”in a “means for” phrase is specifically set forth in the claims, it isnot intended that any elements in the claims be interpreted inaccordance with the specific rules relating to “means for” phraseology.

1. A rear or front projection TV, comprising: an array of micromirrors,wherein the micromirrors comprise micromirror plates that are connectedvia hinges to a substrate, and wherein the substrate, micromirror platesand hinges are disposed in different planes; a light source forproviding light to the array of micromirrors; a screen on which an imageto be viewed is displayed; wherein light from the light source isincident on the array of micromirrors during operation and directed asthe image to be viewed on the screen; wherein the micromirrors arecapable of movement between an OFF state and an ON state by pulse widthmodulation to form the image on the screen; and wherein the micromirrorarray is rectangular with four sides, and wherein each micromirror ofthe array has no micromirror plate sides that are parallel to any of thefour sides of the micromirror array, and wherein light from the lightsource incident on the array of micromirrors is a) substantiallyperpendicular to a side of the micromirror array, b) substantiallyperpendicular to an axis of rotation of the micromirrors, and c) notperpendicular to any micromirror plate sides of the micromirrors.
 2. Theprojection TV of claim 1, further comprising a color wheel.
 3. Theprojection TV of claim 2, further comprising a light pipe.
 4. Theprojection TV of claim 3, wherein the light source is an are lamp. 5.The projection TV of claim 1, which is a rear projection TV.
 6. Theprojection TV of claim 4, which is a front projection TV.
 7. Theprojection TV of claim 5, wherein no micromirror sides are parallel tothe incident light beam when viewed from above the array.
 8. Theprojection TV of claim 5, wherein the micromirrors are positioned suchthat no micromirrors on a lattice are aligned at an angle to horizontaland vertical axes of the rectangular array.
 9. The projection TV ofclaim 1, wherein a first gap is defined between the hinge and themicromirror plate, and a second gap is defined between the micromirrorplate and the substrate.
 10. The projection TV of claim 1, wherein afirst gap is defined between the substrate and the hinge and a secondgap is defined between the hinge and the micromirror plate.
 11. Theprojection TV of claim 5, wherein the array of micromirrors is disposedin a package having a light transmissive window.
 12. The projection TVof claim 11, wherein a mask is provided as part of the package.
 13. Theprojection TV of claim 12, wherein the mask is formed on the packagewindow and extends around a periphery of the micromirror array.
 14. Theprojection TV of claim 11, wherein a molecular scavenger is providedwithin the package.
 15. The projection TV of claim 11, wherein a getteris provided within the package.
 16. The projection TV of claim 11,wherein a source of stiction reducing agent is provided within thepackage.
 17. The projection TV of claim 5, wherein the light beamincident on the micromirror array is from 10 to 50 degrees from a linenormal to the plane of the micromirrors.
 18. The projection TV of claim17, wherein the micromirrors are capable of rotating at least +12degrees to the ON position.
 19. The projection TV of claim 1, furthercomprising a color filter for providing a series of sequential colorsonto the micromirror array.
 20. The projection TV of claim 1, furthercomprising a device for improving the evenness of light distributiononto the micromirror array.
 21. The projection TV of claim 5, furthercomprising optics including a plurality of lenses disposed so as toproject the pattern of light from the micromirror array onto the screen.22. The projection TV of claim 5, further comprising one or more lensesfor directing and focusing a cone of light onto the micromirror array.23. The projection TV of claim 1, further comprising a color wheel, alight pipe and a TIR, prism.
 24. The projection TV of claim 1, whereinthe micromirrors comprise metal and a dielectric material, wherein thedielectric material is a nitride, carbide or oxide of silicon.
 25. Theprojection TV of claim 5, wherein the package is a hermetic package. 26.The projection TV of claim 4, wherein the package is a partiallyhermetic package.
 27. The projection TV of claim 25, wherein themicromirror array is disposed in a package and comprises circuitry andelectrodes on a semiconductor substrate, and bond wires for electricallyconnecting the substrate to the package.
 28. The projection TV of claim4, wherein hinges of the micromirrors extend parallel to leading andtrailing sides of the micromirror array.
 29. The projection TV of claim5, wherein at least 1000 micromirrors are in the micromirror array. 30.The projection TV of claim 5, wherein the micromirrors are tiledtogether.
 31. The projection TV of claim 30, wherein light from thelight source in the form of a beam, of light is directed to a leadingside of the rectangular array at an angle of 90 degrees plus or minus 40degrees.
 32. The projection TV of claim 6, wherein millions ofmicromirrors are provided.
 33. The, projection TV of claim 3, whereineach micromirror has a switching axis substantially parallel to at leastone side of the array.
 34. The projection TV of claim 33, wherein eachmicromirror has a switching axis that is at an angle of from 35 to 60degrees to all sides of the micromirror.
 35. The projection TV of claim33, wherein the light beam is not incident orthogonally to any sides ofthe micrormirrors.
 36. The projection TV of claim 1, wherein eachmicromirror comprises a hinge and micromirror plate that are disposed indifferent planes, and wherein the hinge has a width of from 0.1 to 10um.
 37. The projection TV of claim 1, wherein the thickness of themicromirror plate is from 200 to 7300 angstroms.
 38. The projection TVof claim 1, further comprising a light absorbing layer under themicromirrors to decrease light scatter through the gaps between themicromirrors.
 39. The projection TV of claim 4, wherein from 64,000 to2,000,000 micromirrors are provided in the array.
 40. The projection TVof claim 6, further comprising a TIR, prism.
 41. The projection TV ofclaim 32, wherein from 2,000,000 to 3,000,000 micromirror are providedin the array.
 42. The projection TV of claim 1, wherein the micromirrorarray has an area of from 1 cm² to 1 in².
 43. The projection TV of claim3, wherein the micromirror has a resolution of 1,920,000 or higher. 44.The projection TV of claim 5 having HDTV format.
 45. The projection TVof claim 5, having QXGA format.
 46. The projection TV of claim 5, havingUXGA format.
 47. The projection TV of claim 1, wherein there are nosubstantial micromirror sides that are perpendicular to any array sides.48. The projection TV of claim 1, wherein a horizontal row ofmicromirrors extends corner to corner in the row parallel to a side ofthe rectangular array, and wherein a plurality of vertical linescorresponding to a set of addressing columns extend from eachmicromirror in the row and connect to every other row of micromirrors;and/or wherein a vertical column of micromirrors extends corner tocorner in the column parallel to a side of the rectangular array, andwherein horizontal lines corresponding to addressing rows extend fromeach micromirror in the column and connect to every other column ofmicromirrors.
 49. The projection TV of claim 1, wherein the rectangulararray has two longer sides and two shorter sides, and wherein the lightbeam is incident at a substantially 90 degree angle to a shorter side ofthe rectangular array.
 50. The projection TV of claim 1, wherein themicromirrors are V-shaped.
 51. The projection TV of claim 1, wherein themicromirrors are square.
 52. The projection TV of claim 1, wherein themicromirrors are rectangular.